The present invention relates to sensing the pressure or pressure distribution created between two rigid surfaces.
Pressure sensing devices are typically optimized for sensing the pressure of a fluid like a liquid or a gas. In such a case a single measurement will typically suffice because there is no pressure gradient. When two rigid bodies exert a load on each other a Load-cell is traditionally used. A load-cell measures the total force between the two bodies. Load-cells are typically large and not well suited to being used in an array to sense the uniformity of force between two bodies. Small load-cells are approximately one cubic centimeter. Measuring the pressure distribution across a body with millimeter resolution could not be done with commercial load-cells.
Thin, flexible pressure sensitive sheets exist. The few available products all use a piezoresistive material or some other means to sense the distance between two electrodes separated by an elastomer. The piezoresistive technology is particularly appealing for its low cost. Other gap-sensing approaches can be far more precise and accurate but they are also far more costly. There are a few important problems with the basic scheme. Typically there are performance problems associated with sensitivity, linearity, accuracy, hysterisis, aging, and temperature effects.
A good compromise between cost and performance would be to embed an array of commercial micro-machined pressure sensor die in a thin elastomeric sheet. This approach would solve or greatly reduce many of the previous performance problems.